1. Field of the Invention
The present invention relates to radio communications. More particularly, the present invention relates to a method and apparatus for managing multiple timing advance groups operating with different timings in a Long Term Evolution (LTE) system.
2. Description of the Related Art
With the rapid advance of radio communication technology, the communication system has highly evolved. Long Term Evolution (LTE) is one of the promising 4th generation mobile communication technologies. In an LTE system, various techniques are adopted to meet the explosively increasing traffic demands, and carrier aggregation is one of such techniques. In contrast to legacy LTE systems using a single carrier, between a User Equipment (UE) and an evolved Node B (eNB), LTE systems may use carrier aggregation to flexibly expand available bandwidth by aggregating multiple secondary carriers with a primary carrier. In LTE, the primary carrier is referred to as Primary Cell (PCell) and the secondary carrier as Secondary Cell (SCell).
Meanwhile, for cases in which the locations of the eNB apparatuses using the primary and secondary carriers are different from each other due to the deployment of repeaters and Remote Radio Head, it may be necessary to change the uplink transmission timing. For example, when the eNB apparatus configured with the primary carrier and another eNB apparatus configured with the secondary carrier are located at different places, it may cause problem in transmission timing depending on the location of the UE because the uplink signal addressed to the remote eNB apparatus should be transmitted earlier than the signal addressed to the near eNB apparatus. In such cases, there may exist multiple uplink timings, and it is advantageous for management and reduction of control signaling overhead, to categorize the carriers having the same uplink timing into a group. Such a group is referred to as Timing Advance Group (TAG). Because uplink timing is configured on a per TAG basis, there is a need of a method for managing multiple uplink timings efficiently.
Therefore a need exists for a method and apparatus for managing multiple timing advance groups operating with different timings in a Long Term Evolution (LTE) system.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present invention.